I enjoyed this read, but there are a few issues with it.

The biggest might be that the MC gets isekai'd to a world of skills and stats, but they're playing catch-up and don't seem to have any impact on the MC. It's like he entered the world with max level skills and the system is playing catch-up everytime he does something. Which.. is a different kind of OP?

I liked that the MC wasn't from modern day earth, but rather the flintlock era, which meant the MC had no experience with things like interface, stats, or skills. He rolled with it quickly enough tho, but it meant the story wasn't centered around min/maxing or gaming the system and more the MC just doing what he'd do regardless.

My biggest annoyance however, was when the author seemed to forget what they had previously written. There was one incident where the MC was listening in on an conversation, and overheard that the count had hired an specialist to come and find and kill said MC. But then later, when said assassin shows up to kill the MC. It's like the MC never overheard that they'd ordered a specialist. And pondered who'd send it, assumed it was probably the duke but wanted to see if he could find evidence of such a thing.

Also, for being a master assassin, while he kicks ass and takes names. He does a lot of... questionable things. Like not assassinating the duke when he has the opportunity to do so, and instead does it when it is the hardest. I believe the MC wants the challenge, and is purposely sabotaging himself but it isn't really written that way. For reasons, his logic was he couldn't just kill the duke because then he'd need to flee the city. So he wanted to destabilize the guard first. (but if he just killed the duke, how would they know it was him who did it?)